1. Field of the Invention
The present invention relates to disk drives for computer systems. More particularly, the present invention relates to a disk drive employing error threshold counters to generate an error correction code (ECC) error distribution.
2. Description of the Prior Art
Disk drives comprise one or more disks having a plurality of tracks which are partitioned into a number of data sectors. A head coupled to a distal end of an actuator arm is actuated over the disk to access a target data sector by rotating the actuator arm about a pivot. The user data stored in the data sectors is typically encoded using an error correction code (ECC), such as a Reed-Solomon code, to account for imperfections in the recording/reproduction process. The number of errors that can be corrected using ECC depends on the number of redundancy symbols appended to each data sector. A Reed-Solomon code, for example, can correct up to t erroneous data symbols for every 2t redundancy symbols appended to the data sector.
During the decoding process, the ECC decoder generates 2t error syndromes for use in detecting the location and magnitude of the erroneous symbols in a data sector. If the number of erroneous symbols exceeds the error correction capability of the ECC, the ECC decoder flags the data sector as uncorrectable, and the disk drive performs a retry read of the data sector. Accordingly, prior art ECC decoders only provide an indication as to whether the number of erroneous symbols exceeds the error correction capability of the code. This limited information provides little insight into the actual integrity of the disk drive. That is, knowing only whether a data sector is recoverable using ECC provides no insight into the actual number of data symbols and/or bits in error, which may be useful for various aspects of manufacturing and operation, such as binning disk drives during manufacturing based on quality, selecting a target density per disk (e.g., track density or ECC depth), and in-the-field failure prediction and/or data protection (defect mapping).